Fixed duplicated results in service completion

Author: adamwojs

src/main/java/fr/adrienbrault/idea/symfony2plugin/config/yaml/ServiceYamlReference.java

@@ -18,4 +18,9 @@ public ServiceYamlReference(@NotNull PsiElement psiElement, @NotNull TextRange r
 
         this.serviceId = serviceId;
     }
+
+    @Override
+    public @NotNull Object[] getVariants() {
+        return new Object[0];
+    }
 }